Field of the Invention
The present invention relates to an engine system having two cooling loops including a first coolant loop circulating through an engine and a radiator and a second coolant loop circulating through a low temperature radiator and an exhaust gas recirculation (EGR) cooler.
Description of Related Art
Most diesel engines and some gasoline engines installed in vehicles include an EGR system to cope with exhaust gas regulations.
The EGR system resupplies a portion of an exhaust gas, which is discharged from an engine, through an intake manifold connected to the engine, thus decreasing a combustion temperature of the engine and reducing a generation amount of a nitrogen oxide (NOx).
Here, however, the exhaust gas has a high temperature and high pressure, and thus, when it is resupplied in the high temperature state, without being cooled, to the engine, the effect of reducing the generation amount of the nitrogen oxide (NOx), the original purpose of the EGR system, may be insufficient.
That is, the EGR system reduces a temperature of the exhaust gas through a heat exchanger in which a coolant circulates, and resupplies the exhaust gas having a reduced temperature to the engine through the intake manifold, thus reducing a generation amount of the nitrogen oxide.
An engine coolant circulating in the engine reaches about 90° C. and the recirculating exhaust gas reaches about 600° C., and thus, there is a limitation in stably cooling the recirculating exhaust gas using the engine coolant.
In order to overcome such a limitation, the recirculating exhaust gas may be cooled using a low temperature coolant (about 45° C.) for a water-cooled intercooler. In this case, however, the EGR cooler may be excessively cooled by the low temperature coolant so as to be damaged.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.